Conventionally, in microwave-assisted magnetic recording (MAMR) systems, a high-frequency magnetic field is applied to a magnetic recording medium while recording to temporarily weaken the coercive force of the recording area by using the resonance phenomenon of the medium. This is referred to as microwave-assisted because the resonance frequency of the medium is in the microwave band. Recently, the use of a microwave magnetic field oscillation layer, referred to as a spin torque oscillator (STO), for rotating the magnetization at high speed by using spin torque has gained popularity, and MAMR has become a focus of attention. In addition, the idea of using the magnetic field of the main pole adjacent to the STO to control the direction of rotation of the oscillation has been utilized, and MAMR is becoming more and more practical.
In MAMR, the STO controls the pulsing of the oscillations by the pulsing of a bias current (on/off state function). However, the STO is not limited to this normal operating state in a hard disk drive (HDD) or other magnetic storage device which utilizes MAMR. For example, because recording on a hard disk of a HDD is particularly difficult at low temperatures, the STO may be used in the “on state” only at low temperatures. In another example, the use of the STO in the “on state” may occur only when recording errors occur during a repeated write (referred to as a “retry”).
A MAMR head is a structure in which a STO is deposited in a layer on a conventional recording main pole. However, because of manufacturing errors which may occur, the position of the STO does not necessarily align with the main pole (off-alignment). Alternately, the STO is sometimes larger than the main pole. In this case, there is concern that the recording width will differ when the STO is in the on state or the off state. For example, as shown in the SEM photograph in FIG. 5, when the STO is offset to a right side with respect to the main pole, the recording width will sometimes become wider on the right side when the STO is in the on state as indicated by the bathtub curve (which is the error rate profile in a track width direction), shown in FIG. 6. As shown in FIG. 7, one reason for this phenomenon is that the recording width is determined by the STO in addition to the main pole when the STO is in the on state, in contrast to the recording width in the medium being determined by the main pole width when the STO is in the off state.
Recently, as HDDs utilizing shingled magnetic recording (SMR) systems have approached commercialization, the structures of these HDDs are based on SMR even when utilizing MAMR. When the recording width is changed as described above, one issue appears where the destruction of data in adjacent tracks occurs due to the changing recording width. In normal SMR, overwrites are conducted while the recording head is shifted by a constant track pitch. However, when the shift quantity is constant, regardless of widening of the recording width which may occur in MAMR systems, as shown in FIG. 8, the immediately preceding written data are destroyed.
Accordingly, it would be beneficial to have a MAMR-SMR system which rectifies the issues with the written data being destroyed in adjacent tracks due to recording width variations.